Grouping similar rows next to each other in MySQL

Question

I have no idea how to explain this well, so please bear with me.

I am trying to group similar rows that are right next to each other, essentially ignoring the n+1th

Answer 1

You can do this by using a clever trick. The trick is to count the number of descriptions up to a particular id that are different from the description at that id. For values in a sequence, this number will be the same.

In MySQL you can do this count using a correlated subquery. The rest is just grouping by this field to bring the values together:

select min(id) as id, description, count(*) as numCondensed
from (select t.*,
             (select count(*)
              from table t2
              where t2.id <= t.id and t2.description <> t.description
             ) as grp
      from table t
     ) t
group by description, grp;